The invention relates to a magnetic component.
Magnetic components (coils or transformers) are also provided for use in high frequency clocked electronic circuits, for example, parts of combinatorial circuits. In many electronic devices of the consumer electronics industry, parts of combinatorial circuits are used nowadays. A large problem is then caused by the electromagnetic disturbances resulting from the high-frequency switching mode. This problem becomes particularly serious when the parts of combinatorial circuits are built-in in monitors, television sets or audio sets, because the video and audio quality respectively may be influenced. More particularly radio reception is strongly affected in the long-wave and medium-wave range, because this frequency range lies in the neighborhood of switching frequencies or their first harmonics. To the most important noise sources belong the magnetic components which generate a very strong magnetic stray field.
A method usually implemented for reducing this magnetic stray field comprises creating a short-circuit winding around the coil or the transformer respectively, with the aid of a conductive foil, usually a copper strip. This method, however, is not at all sufficient for lowering the magnetic field to a level that is no longer detected by the medium-wave antenna of the audio device. A further efficient method comprises that the magnetic component is built-in in a closed screen housing. Added to the disadvantage of extra cost and weight is here particularly the poorer heat dissipation.
From WO 81/02648 (compare its FIG. 1) is known a magnetic component with a U core in which a winding is deposited on two opposite core limbs. When there is a current flowing through the windings, the generated stray fields are mutually partly compensating so that the resulting stray field outside the magnetic component is reduced.
It is an object of the invention to provide a further variant for a magnetic component, in which the generated stray field outside the component is minimized.
The object is achieved in that at least two windings electrically connected in series are provided and in that the magnetic component has a core on which the windings are arranged so that in the case of a current flowing through the windings, the generated magnetic stray fields outside the component at least partly compensate each other, while the core has at least one inside limb portion and at least two outside limb portions and the windings are arranged on the inside limb portion and/or the outside limb portions.
The desired effect of stray field reduction outside the magnetic component can be obtained with the aid of cores for magnetic components, for example, E or P cores which are customary in the market. A winding is then suitably subdivided so that spatially separated winding portions are formed which are no longer directly magnetically coupled i.e. the same magnetic flow no longer passes through them. Outside the magnetic component, an effective compensation of the magnetic fields generated by the respective windings can thus be achieved, so that the resulting magnetic stray field outside the component is largely minimized. There are component variants which can be manufactured cost effectively and effectively reduce the stray field. More particularly, the individual windings have, in essence, equal inductance values, so that with symmetrical component structures an optimum compensation of the generated stray fields outside the magnetic component is achieved. With asymmetric arrangements, however, different inductance values may regularly be selected.
In an embodiment of the invention, there are two cores which have corresponding inside and outside limb portions. The inside limb portions carry each a winding for guiding a magnetic flow and between the two core portions a third core portion is arranged which is I-shaped in cross-section. This embodiment is preferably realized by means of an E core between whose core halves the core portion having an I shape in cross-section is arranged.
Another variant of embodiment of the invention provides that two inside core portions are provided which have corresponding inside and outside limb portions pointing inwards, that on the outside of the inside core portions further core portions are arranged which have further inside and outside limb portions corresponding to the inside and outside limb portions of the inner core portions and that the windings are arranged on the inside core portions. This embodiment provides a further improved reduction of the stray field outside the magnetic component. The component core is preferably realized by means of two E cores i.e. by means of four E core halves lying on top of each other, whose inside and outside limb portions all point to the inside of the component.
A further reduction of the outside stray field may be achieved in that the outside limb portions of the core portions carry at least part of the windings. When the inside and outside limb portions of the core portions then carry windings, the stray field reduction is optimized further. The idea according to the invention, however, also includes the case where only the outside limbs carry windings. The invention also relates to a core for one of the variants of a magnetic component described above.